The making and using of pozzolanic cementitious products is an old art practiced by the Egyptians as well as the Romans. Pozzolanic cementitious products were widely used until the early 1940's when it became evident that the pozzolans had a slower strength gain and lacked workability in comparison to cement without pozzolans.
Cement continued to be ground finer and this along with the refining of the calcining process allowed for extremely workable pozzolan-free cements with good strength. Unfortunately, these beneficial increases were accompanied by an increase in calcium hydroxide which is the weakest constituent of a cement. An increase in calcium hydroxide meant an increase in aggressive attack of the cement. In the 1960's, the industry renewed its interest in pozzolanic cements.
Pozzolans are generally high in siliceous or in siliceous and aluminous materials. The chemical and physical mechanisms by which pozzolans react with cement to affect the properties of the resulting cementitious products are not fully understood although it is known that pozzolans usually have no cementing properties of their own. It is believed that the benefit pozzolans brought to cementitious products resulted from their ability to combine with free lime or calcium hydroxide in cement to create an insoluble compound having cementing properties.
Thus, an important benefit that pozzolans offered to cementitious products was their ability to react with calcium hydroxide thereby rendering the cementitious product more durable than otherwise possible. However, some pozzolanic constituents reacted slower than others and while they improved the resistance of the cementitious product to aggressive water attack, the improvement did not come soon enough for some applications, especially those cementitious products which were to be used in water contact situations, such as but not limited to bridge and pool construction. Other pozzolanic constituents reacted faster, but the cementitious products made with these pozzolanic constituents were generally not very durable. What was needed was a pozzolanic mixture which exhibited both a fast reaction, and resulted in workable, durable cementitious products.
Pozzolans include a wide variety of materials, naturally occurring and artificial. Each pozzolanic material possesses different properties and as a result, performs differently with cement depending on many variables. The fineness of the pozzolan, the degree with which a pozzolan is calcined, and the chemical and physical make-up of the pozzolan, are just a few of the variables of the pozzolanic component of a cementitious product which render no two pozzolan cementitious products alike. The resulting performance of each pozzolan in a cementitious product must therefore be analyzed for the effect desired, because there is no sure way to predict how a given pozzolan cement will perform until it is formulated and tested.
Some of the prior pozzolanic cementitious products like Mehta, U.S. Pat. No. 5,346,548 (1994), and, Turpin, Jr., U.S. Pat. No. 4,313,763 (1982), which used slag pozzolans or fly ash pozzolans, suffered from an aesthetically offensive dark color which the pozzolans imparted to the resulting product. Darkly colored cementitious products are unacceptable for many applications where a light colored cementitious product is desired. One example of where light colored cementitious products are highly desired is in swimming pool construction because dark pools create the feeling that the water is dirty. Because no light colored pozzolanic cementitious products are presently available, today's pools are constructed with non-pozzolanic cementitious products foregoing all the benefits that pozzolanic cementitious products have to offer.
Other prior art pozzolan cementitious products are taught by Jesky, U.S. Pat. No. 3,982,954 (1976), and, Turpin, Jr., U.S. Pat. No. 4,256,500 (1981), both of whom add a single pozzolan component to a cementitious product. Bainton, U.S. Pat. No. 3,953,222 (1976) teaches the acidation of a pozzolan prior to mixing with cement. Other references which teach the combination of cement and a pozzolan to produce materials other than cement are Walter et al., U.S. Pat. No. 5,324,469 (1994); and Turner, U.S. Pat. No. 5,391,245 (1995). None of these teach the use of a plurality of pozzolanic materials to form a superior pozzolanic combination which when admixed with cement, will optimize the desirable properties of the resulting cementitious product. Lower permeability, greater workability, quicker strength recovery, high resistance to chemical and water attack, and lower heat of hydration will be realized. A cementitious product which optimizes all of these desirable properties is still lacking in the art. It is to this end the present invention is directed.